Globally is the water production associated with the oil & gas production more than three times higher than the oil production. This gives an average water fraction of about 75% of what is produced from the wells. The water percentage continues to increase. About ten years ago was it about 70%. The water fraction increases in proportion to the oil fields being older and decreases in proportion to better methods being developed to handle the reservoir and to new fields being introduced. Simultaneously the environmental conditions are being more strict and more complicated to meet. The challenges for the operators are increasing and the need of better, diminished and more cost effective technologies arises. The costs of water treatment participates in determining how high water content it will be profitable to produce. This will also depend on the oil price.
The purpose of the present invention is to provide a purification system for produced water with the main focus at oil installations onshore and offshore worldwide. Produced water coming up from the well with the well stream is separated from the oil and gas, and then purified and discharged to the sea or reinjected into the reservoir. Produced water is a mixture of formation water, residuals of production chemicals and reinjected water (on installations where this is carried out). The contents and composition of produced water vary from field to field and from well to well within the same field. In addition will also the composition vary over time in one and the same well. Each minute will Norwegian oil platforms treat about 400 m3 water. A constantly more mature Norwegian shelf with less oil and more water has resulted in a strong increase in produced water. In 2007 about 200 million m3 produced water were treated on the Norwegian shelf. About 90 percent of this was discharged to the sea.